The present invention relates to polishing pads used for chemical-mechanical polishing of substrates. More particularly, the present invention relates to polishing pads having modified groove dimensions to produce a more uniformly polished substrate surface.
Chemical mechanical polishing (sometimes referred to as "CMP") typically involves mounting a substrate faced down on a holder and rotating the substrate face against a polishing pad mounted on a platen, which in turn is rotating or is in orbital state. A slurry containing a chemical component that chemically interacts with the facing substrate layer and an abrasive component that physically removes that layer is flowed between the substrate and the polishing pad or on the pad near the substrate. In semiconductor wafer fabrication, this technique is commonly applied to planarize various wafer layers such as dielectric layers, metallization layers, etc.
FIG. 1A shows a front view of a polishing pad 10, e.g., IC 1000 available from Rodel of Newark, Del., that is employed in modem CMP systems, such as the AvantGaard 676 available from Integrated Processing Equipment Corporation (IPEC) of Phoenix, Ariz. A surface of polishing pad 10 includes a plurality of macrogrooves 12, microgrooves 14 and slurry injection holes 16. Macrogrooves 12 are shown in an X-Y configuration, i.e. vertical and horizontal macrogrooves intersect at various points to form a "grid", microgrooves 14 are oriented substantially diagonally relative to macrogrooves 12 and slurry injection holes 16 are positioned at various intersections of the vertical and horizontal macrogrooves 12. FIG. 1C shows a cross-sectional view of a macrogroove 12 of FIG. 1A, which macrogroove is shaped like a square channel with sharp comers having a width (labeled "w") and a depth (labeled "d").
Those skilled in the art will recognize that microgrooves 14 are different from the grooves formed during conditioning of the polishing pad. Microgrooves 14 are formed by a polishing pad manufacturer during the fabrication of the polishing pad. Furthermore, microgrooves 14 of FIG. 1A are not limited to any particular configuration and may be obtained by a polishing pad manufacturer in other configurations. By way of example, FIG. 1B shows a surface of a polishing pad 20, which is also available from Rodel and typically employed in a conventional CMP system such as the Avanti 472 also available from Integrated Processing Equipment Corporation. Polishing pad 20 includes microgrooves 22 that are arranged in a spiral configuration and facilitate slurry flow.
The macrogroove dimensions of width and depth are typically larger than those of microgrooves. By way of example, macrogrooves 12 in the X-Y configuration shown in FIG. 1A typically have a width and depth of about 1 mm and microgrooves 14 typically have a width and depth that is about 250 .mu.m. As another example, microgrooves 22 in the spiral configuration as shown in FIG. 1B typically have a width that is between about 100 .mu.m and about 400 .mu.m and a depth that is about 250 .mu.m.
During a typical CMP process on the polishing pad surface of FIGS. 1A, slurry is introduced on the polishing pad surface via slurry injection holes that are in communication with a slurry reservoir. The "channel" shaped macrogooves facilitate slurry flow or distribution throughout the polishing pad surface. The rotating action of a substrate on the polishing pad picks-up some slurry from the macrogrooves and spills it on the microgrooves. As a result, a portion of slurry is dispersed between the polishing pad and substrate interface. A film on the substrate surface is removed by chemical and mechanical interaction with the slurry dispersed above microgroove.
After polishing on the same polishing pad over a period of time, however, the polishing pad suffers from "pad glazing." Pad glazing results when the particles eroded from the substrate surface along with the abrasives in the slurry tend to glaze or accumulate over the polishing pad. In order to remove this glaze, the polishing pad undergoes conditioning (hereinafter referred to as "pad conditioning") by a conditioning sub-assembly either every time after a substrate has been polished or simultaneously during substrate CMP.
A conditioning sub-assembly incorporated into the AvantGaard 676, for example, includes a conditioning arm having a conditioning surface with abrasive particles. During pad conditioning the conditioning arm forcibly sweeps back and forth across the polishing pad like a "windshield wiper blade" and a pneumatic cylinder applies a downward force on the conditioning arm such that the abrasive particles of the conditioning surface engage the polishing pad to remove the glaze and roughen up the polishing by introducing grooves or perforations on it.
Unfortunately, during the normal course of the polishing pad life, typically some areas of the polishing pad begin to erode (also known in the art as "pad erosion") or wear out due to the repeated abrasive action by the abrasive particles of the conditioning surface during conditioning and the repeated mechanical action of the substrate during CMP. In these worn out areas, the "channel" shape of the macrogrooves or microgrooves degrades sufficiently so that the macrogrooves are no longer effective in transporting slurry on the polishing pad surface. By way of example, in the AvantGaard 676, a center area of the polishing pad is relatively more worn out, e.g., the channel shape of the macrogrooves degrades to a greater extent in this area, than other areas of the polishing pad because the substrate contacts the center area of the polishing pad most of the time during CMP. As a result, there is nonuniform slurry flow on the polishing pad surface and the substrate surface suffers from a non-uniform film removal rate, which lowers the yield of the polished substrates.
What is therefore needed is an improved polishing pad design for effective slurry transport to produce a uniformly polished substrate surface.